JavaScript 相当于 Perl 的 AUTOLOAD

发布于 2024-10-26 17:55:57 字数 488 浏览 4 评论 0原文

我想我可能会在谷歌搜索中失败，也许这种模式不适合 JavaScript 处理 MRO 的方式，但我正在寻找与 Perl 的 AUTOLOAD 方法等效的方法，这样：

function car() {
  return {
    start: function() { alert('vrooom') },
    catchall: function() { alert('car does not do that'); }
  }
};

car().start(); //vrooom
car().growBeard(); //car does not do that

在 Perl 中快速处理这种情况我会写：

sub AUTOLOAD { __PACKAGE__." doesn't do that" }

但是我无法理解 JavaScript 中捕获未定义方法的语法。也许重载 .call 或 .apply 之类的？

原文

I think I might fail at Googling, and maybe this pattern just doesn't fit with the way JavaScript handles MRO, but I'm looking for an equivalent to Perl's AUTOLOAD method such that:

function car() {
  return {
    start: function() { alert('vrooom') },
    catchall: function() { alert('car does not do that'); }
  }
};

car().start(); //vrooom
car().growBeard(); //car does not do that

in Perl to quickly handle this situation I'd write:

sub AUTOLOAD { __PACKAGE__." doesn't do that" }

but the syntax to catch an undefined method in JavaScript eludes me.
Perhaps overloading .call or .apply or something?

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云仙小弟 2024-11-02 17:55:57

如果您只是想知道是否定义了某个方法，您可以执行以下操作：

if(car().growBeard){
}

听起来您要找的是 __noSuchMethod__ ，但是它仅在 mozilla 中受支持，而不是正式 ECMAScript 规范的一部分。

function car() {
  return {
    start: function() { alert('vrooom'); },
    __noSuchMethod__ : function (){alert('no method');}
  };
}

jsfiddle 上的 __noSuchMethod__ 示例，仅适用于基于 mozilla 的浏览器。

使用简单的异常处理，您也许能够获得所需的行为：

try {
    car().start(); //vrooom
    car().growBeard();
}
catch (e) {
    if (e instanceof TypeError) {
        alert(e.message);
    }
}

If you simply want to know if a method is defined you can do the following:

if(car().growBeard){
}

It sounds like what you are looking for is __noSuchMethod__, however it is only supported in mozilla, and not part of the formal ECMAScript specifications.

function car() {
  return {
    start: function() { alert('vrooom'); },
    __noSuchMethod__ : function (){alert('no method');}
  };
}

Example of __noSuchMethod__ on jsfiddle, only works in a mozilla based browser.

Using simple exception handling you might be able to get your desired behavior:

try {
    car().start(); //vrooom
    car().growBeard();
}
catch (e) {
    if (e instanceof TypeError) {
        alert(e.message);
    }
}

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静若繁花 2024-11-02 17:55:57

新的 ES6 代理对象将有所帮助：（从此处复制的示例代码）

obj = new Proxy({}, {
  get: function(target, prop) {
    if (target[prop] === undefined)
      return function() {
        console.log('an otherwise undefined function!!');
      };
    else
      return target[prop];
  }
});
obj.f() // "an otherwise undefined function!!"
obj.l = function() { console.log(45); };
obj.l(); // "45"

代理对象是不可调整的。浏览器支持很好，但还不完美，请参阅 http://caniuse.com/#feat=proxy。

The newish ES6 Proxy object will help: (sample code copied from here)

obj = new Proxy({}, {
  get: function(target, prop) {
    if (target[prop] === undefined)
      return function() {
        console.log('an otherwise undefined function!!');
      };
    else
      return target[prop];
  }
});
obj.f() // "an otherwise undefined function!!"
obj.l = function() { console.log(45); };
obj.l(); // "45"

Proxy objects are unshimmable. Browser support is good, but not perfect yet, see http://caniuse.com/#feat=proxy.

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